A typical wireless communication system includes one or more base stations, each radiating to define one or more coverage areas, such as cells and cell sectors, in which wireless client devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. Further, each base station of the system may then be coupled or communicatively linked with core network infrastructure such as a switch or gateway that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the system may thus engage in air interface communication with a base station and thereby communicate via the base station with various remote network entities or with other WCDs served by the system.
In general, a wireless communication system may operate in accordance with a particular air interface protocol or radio access technology, with communications from a base station to WCDs defining a downlink or forward link and communications from the WCDs to the base station defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Long Term Evolution (LTE) (using Orthogonal Frequency Division Multiple Access (OFDMA) and Single-Carrier Frequency Division Multiple Access (SC-FDMA), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communication (GSM), WI-FI, and BLUETOOTH. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each of the one or more coverage areas of such a system may operate on one or more carrier frequencies (carriers) and may define a number of air interface channels for carrying information between the base station and WCDs. By way of example, each coverage area may define a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that WCDs may detect as an indication of coverage and may measure to evaluate coverage strength. Further, each coverage area may define a downlink control channel for carrying system information, page messages, and other control signaling from the base station to WCDs, and an uplink control channel for carrying service requests and other control signaling from WCDs to the base station, and each coverage area may define downlink and uplink traffic channels or the like for carrying bearer traffic between the base station and WCDs.
When a WCD first powers on or otherwise enters into coverage of such a system, the WCD could search for a strongest coverage area in which to operate and could then engage in signaling to acquire wireless connectivity with the base station that provides the coverage area. The WCD could then be served by the base station in a connected mode or an idle mode.
In the connected mode, the WCD may have a radio-link-layer connection with the base station, over which to engage in user-plane communication such as transmission/reception of bearer data (e.g., application-layer data). Thus, as user-plane traffic arrives at the base station for transmission to the WCD, the base station could coordinate transmission of that traffic over the air to the WCD, and as the WCD has user-plane traffic to transmit via the base station, the base station could coordinate transmission of that traffic over the air from the WCD. And in the idle mode, the WCD may lack a radio-link-layer connection but may monitor for pages from the base station and may transition to the connected mode when necessary to engage in user-plane communication.
While so served, the WCD may also monitor coverage strength from its serving base station and from adjacent base stations, to help ensure that the WCD is served with sufficiently strong coverage and perhaps with the strongest available coverage. If the WCD's coverage from its serving base station becomes threshold weak and if another base station's coverage becomes threshold strong (e.g., threshold stronger than the serving base station's coverage), the WCD may engage in signaling with its serving base station, and the serving base station may take action to coordinate handover of the WCD to the other base station.
Optimally, a wireless service provider will strategically implement base stations throughout a market area so that served WCDs can transition between the base stations' coverage areas without loss of coverage. Each base station may include an antenna structure and associated equipment, and the service provider may connect each base station by a landline cable (e.g., a T1 line) with the service provider's core network, to enable the base station to communicate on that network.
In certain locations, however, it may be impractical for a wireless service provider to run landline connections to base stations. For instance, where a service provider seeks to provide many small coverage areas blanketing a market area or to fill in coverage holes between coverage of other base stations, the service provider may implement many small-cell base stations throughout the market area, but it may be inefficient or undesirable to run landline cables to every one of those small-cell base stations.
To provide coverage in such locations, the wireless service provider may instead implement relays, each of which could be configured to operate in much the same way as a conventional landline-connected base station but could have a wireless backhaul connection to a core network. In particular, each relay could include a relay base station and an associated relay-WCD module (integrated or communicatively linked together). The relay-WCD module, and thus the relay, could then be served by an existing base station of the network, referred to as a donor base station, with the air interface between the relay-WCD and the donor base station defining a wireless backhaul connection for the relay. With this arrangement, the relay could thus conveniently communicate with the core network via the wireless backhaul connection and the donor base station.